1. Field of the Invention
This invention relates to a process for producing a copper alloy, and, more particularly, it is concerned with a process, by which Cu-Ni-P-Si alloy and Cu-Ni-P-Si-Zn alloy which are most suitable copper alloy as a lead frame material for integrated circuits, connectors, relays, and so on for electronic apparatuses and appliances.
2. Discussion of Background
As a method for producing an ingot of copper alloy for electronic apparatuses and appliances, there has so far been practiced generally the continuous casting by means of a horizontal continuous casting device. FIG. 2 of the accompanying drawing is a cross-sectional view of the conventional horizontal continuous casting device as disclosed in, for example, Japanese Unexamined Patent Publication No. 39639/1983. In this figure of drawing, a reference numeral 1 designates a melt of a metal which has been melted in a melting furnace (not shown in the drawing) by electric power such as, for example, high frequency electric power; a numeral 2 refers to a holding furnace to retain therein the melt 1 at a certain definite temperature level and in a required quantity; a numeral 3 refers to a graphite mold which is fixedly provided at the lower end part of the holding furnace 2; a reference numeral 4 denotes a water-cooling jacket which is provided in a manner to surround the graphite mold 3; and a reference numeral 5 represents traction rollers for drawing an ingot 6 obtained by cooling and solidifying the melt 1.
In the casting device of the above-mentioned construction, the melt 1 which is collected in the holding furnace 2 is poured into the graphite mold 3 and solidified under the cooling action of the cooling water flowing in the water path in the interior of the water-cooling jacket 3, and the thus solidified metal is discharged from the casting mold 3 in the form of an ingot 6. In this case, the ingot 6 is drawn out by the traction rollers 5 either continuously or intermittently, whereby a continuous web of the ingot 6 is obtained. After this, rolling and heating of the ingot are repeated to finish the ingot into a thin plate material of a predetermined size.
In the case of casting a melt of an alloy of a type which is strengthened, in accordance with the above-mentioned casting method, by dispersing and depositing an intermetallic compound into a matrix, the ingot is in the state of its containing therein the intermetallic compound which is non-uniformly dispersed in the matrix, the intermetallic compound to be formed in the course of its solidification having a coarse and irregular grain size, on account of a relatively low cooling rate of 10.degree. C./min. or below. With the ingot of such state, the size and the dispersed state of the intermetallic compound is not substantially changed from its state as cast, even when it is finished into the ultimate thin plate product through the process steps of heating and rolling to take place after the casting. As the result, while excellent mechanical strength and favorable electrical conductivity can be obtained with the thin plate product, it is considerably inferior in its shapability with the consequent problem of its being inapplicable to the field of electrical connectors where the stringent shaping capability is demanded.
Further, the presence of the intermetallic compound in coarse grain size leads to non-uniform etching, blistering and peeling of the plated portion, and moreover poor bonding in the bare bonding (i.e., connection of a copper type lead frame material and a semiconductor chip with a wire of Au, Al or Cu), which possibly brings about decrease in reliability of the alloy for the electronic parts.